1. Field of the Invention
The present invention relates to a thin film transistor (TFT), a method of manufacturing the thin film transistor, and a flat panel display (FPD) device including the thin film transistor, and more particularly, to a TFT using oxide semiconductor as an active layer, a method of manufacturing the thin film transistor (TFT), and a FPD device including the thin film transistor (TFT).
2. Description of the Related Art
In general, a thin film transistor (TFT) includes an active layer which provides a channel region, a source region and a drain region, and a gate electrode electrically insulated from the active layer by an insulating layer with the gate electrode being formed on the channel region.
The active layer of the TFT having the above mentioned structure may be formed of a semiconductor material such as amorphous silicon or poly-silicon. When the active layer is formed of the amorphous silicon, the mobility of the TFT is relatively low so that it is difficult to realize a driving circuit that operates at a high speed. When the active layer is formed of the poly-silicon, even though the mobility of the TFT is relatively high, a threshold voltage may be disadvantageously non-uniform so that an additional compensating circuit is required.
In addition, in a contemporary method of manufacturing the TFT using low temperature poly-silicon (LTPS), because an expensive process such as a laser heat treatment may be included and may be difficult to control characteristics, it is difficult to apply the expensive method to fabricate TFT on a large area substrate.
Recently, in order to solve the above stated problems, research has been performed to employ an oxide semiconductor as the active layer.
In Japanese Patent Publication No. 2004-273614, a TFT using oxide semiconductor in which Zinc Oxide (ZnO) is a main component as an active layer is disclosed.
The oxide semiconductor in which the ZnO is the main component is evaluated as an amorphous and stable material. When the oxide semiconductor is employed to form the active layer, it is possible to manufacture the TFT by using the low temperature poly-silicon (LTPS) process at a low temperature not higher than 300° C.
In order to apply the oxide semiconductor in which the ZnO is the main component to during fabricating the TFT, however, it is necessary to develop a process to enhance an electric characteristic of the TFT and thus improving the electric characteristic of the TFT.